General Viele's map of
Manhattan Island (Plate IX[D]), with the points where difficulties in
the construction of the tunnels were encountered has been noted in a
previous paper.

In all cases where the course of this ancient stream was crossed (except
at its final intersection of 33d Street), the rock was found to be very
soft and disintegrated, a large quantity of water was encountered, and
heavy timbering was required. The construction at these localities will
be taken up later. In addition, disintegrated rock, but of a less
troublesome character, was invariably met under the depressions in the
rock surface developed by the borings from the streets and test holes
from the tunnels. Many of these places required timbering, and no
timbering was elsewhere necessary except at the portals. These
coincident conditions were especially marked in 32d Street, which for a
long distance closely adjoins the course of the former creek.

_Disposal of Spoil._--The materials excavated from the tunnels were
dumped at the 35th Street pier on barges furnished by the Railroad
Company under another contract, and were towed to points near the
Bayonne peninsula where the spoil was used principally in the
construction of the Greenville Freight Yards and the line across the
Hackensack Meadows to the tunnels. Details of this work will be given in
a subsequent paper. After December, 1907, when the excavation was about
85% completed, the contractor furnished the barges and effected the
complete disposal of the spoil.

_Difficulties of Excavation._--As stated in a previous paper, the
excavation of the Twin Tunnel in 33d Street was continued westward to
the west line of Fifth Avenue on the original grade. At that point the
contractor started three drifts in the three-track section. The relation
of the drifts to each other and to the cross-section are shown by Fig. 3.
The center heading was driven a little in advance of those on the
sides. At a distance of 65 ft. west of Fifth Avenue the rock surface was
broken through in the top of the heading, and a very fine sand was
encountered. For some distance east of this point the rock was badly
disintegrated, and the heading required timbering. Through the soft
material, tight lagging was placed on the sides and roof of the heading,
and the face was protected by breast boards. There was a moderate flow
of water through the cracks, and, in spite of every effort, some of the
fine sand was constantly carri